The present invention relates generally to an image forming apparatus such as an electrophotographic or electrostatic recording-type copier, printer or the like that adheres a developer to a potential image formed on an image carrying medium so as to turn the potential image into a visible image, and more particularly, to an image forming apparatus equipped with a developer control unit for adjusting the density of a two-part toner, and an image forming method thereof.
Generally, in a developing apparatus equipped with an electrophotographic or electrostatic recording-type image forming apparatus, a two-part developer consisting of toner particles and carrier particles is used. Particularly with color image forming apparatuses that use electrophotography to form a full color or multi-color image, most of the developing apparatuses use a two-part developer.
FIG. 1 shows a schematic cross-sectional view of a conventional two-part developing apparatus. Numeral 10 denotes a developer container; numeral 2 denotes the developing sleeve. The developing sleeve 2 is an empty metallic sleeve, within which is contained a magnetic roller 3 that constitutes a magnetic field generating means. Two agitation devices that are screws A and B are arranged inside the developer container 10. The A screw 5 is disposed substantially parallel to the developing sleeve 2, with B screw 6 disposed on the opposite side of A screw 5, away from the developing sleeve 2.
FIG. 2 shows a plan view of a conventional developing apparatus. As shown in the diagram, the A screw 5 and the B screw 6 are disposed substantially parallel to each other in a latitudinal direction, with an inner wall 7 is disposed between the A screw 5 and the B screw 6 so as to prevent the developer from getting directly in between the two screws A and B. It will be noted that the inner wall 7 does not extend all the way to the longitudinal ends, so that the developer is able to travel between the two screws A and B. The two screws A and B are set to churn the developer in opposite directions. A gear not shown in the diagram connects the developing sleeve and the two screws A and B. When the developing sleeve 2 rotates, the developer circulates continuously within the container in the direction of the arrows.
As is commonly known, the toner density of a two-part developer, that is, the ratio of the weight of the toner particles to the total weight of the carrier particles and toner particles combined is an extremely important factor in stabilizing the image quality. The developer toner particles are consumed during development, so the toner density changes. As a result, it is necessary to use a toner density control unit (ATR) to detect the developer toner density accurately in a timely manner and to replenish the toner as the density changes in order to maintain the toner density at a uniform level and thereby to maintain the quality of the image.
In order to compensate for these changes in the density of the toner inside the developing apparatus as the developing process progresses, it is necessary to control the amount of toner supplied to the developing apparatus. Toward this end, a variety of systems have conventionally been used for the toner density detection apparatus and the density control apparatus.
For example, there are developer density control apparatuses that make use of the fact that the reflectance of light brought near to the developer holder (typically a developing sleeve is often used for this purpose, so hereinafter the developer holder is referred to as the xe2x80x9cdeveloping sleevexe2x80x9d), or a developer transport path of the developer container and directed onto transported developer located atop the developing sleeve or the developer inside the developer container differs according to the toner density to detect and control the toner density. Additionally, there are inductance detection-type developer density control apparatuses that use detection signals from an inductance head that detects a nominal magnetic permeability from the relative proportions of the magnetic carrier and the nonmagnetic toner sticking to the side walls of the developer container and converts the detected magnetic permeability into an electrical signal in order to detect the actual density of the toner inside the developer container, and to supply toner based on a comparison of the detected density with some reference value.
Additionally, there are systems in which a patch image density formed on an image retaining body (typically a photosensitive drum is often used for this purpose, so the image retaining body is hereinafter is referred to as a xe2x80x9cphotosensitive drumxe2x80x9d) is acquired by a sensor that receives light directly or via reflection from a light source disposed opposite the surface of the photosensitive drum, the acquired patch image density is converted to a digital signal by an analog-digital converter and transmitted to a CPU, and the CPU then cuts off the supply of toner until the indicated reading returned to an initial preset value if the read density is higher than such initial preset value, as a result of which the toner density is maintained indirectly at a desired value.
However, there is a drawback to the system for detecting toner density from the reflectance of light directed onto either the transported developer located atop the developing sleeve or the developer inside the developer container, in that accurate toner density readings cannot be obtained if the toner dirties the detecting means.
Similarly, there is a drawback to the inductance detection-type ATR, in that the sensor detection signals change discontinuously due to changes in the apparent density of the developer due to fluctuations in the disposition and environment directly before the image forming apparatus stops operation and directly after the image forming apparatus recommences operation.
Similarly, there is a drawback to the system for controlling toner density indirectly from the patch image density, in that if the patch density measurements are taken too infrequently the intervening toner densities cannot be gauged accurately, whereas if the measurements are taken too frequently the print is interrupted and consequently the number of sheets of paper output cannot be accurately determined. Additionally, as the image forming apparatus is made compact, the space needed to form the patch image or provide the detecting means cannot be retained.
Accordingly, as a method that eliminates the above-described drawbacks, a toner supply system that utilizes a video count has been commercialized.
According to such a system, in order to maintain the toner density at a constant level inside the developer container as the density decreases through developing, the output levels of the digital image signals of each of the pixels are integrated to obtain a print ratio for the image, which is used to calculate the amount of toner to be consumed and thus to be supplied. In other words, from the signals input to a laser scanner or other such exposure device, the exposure output level for each of the pixels is integrated, converted to a video count factor and then transmitted to the CPU. The CPU converts the video count factor to a supply volume, transmits a toner supply signal to activate a toner supply unit, and supplies the required amount of toner to the interior of the developer container, thus maintaining the density of the toner inside the developer container at a constant level.
FIG. 3 is a flowchart of steps in the conventional process of video count-based toner supply, and FIG. 4 is a corresponding timing chart thereto. The main power supply indicates the ON-OFF status of the main power supply for the image forming apparatus, and the print operation denotes the status of operations relating to the image output (S806). The developer unit rotation refers to the rotational state (S807) of the developing sleeve and agitation devices. The exposure device drive refers to a state (S808) in which an exposure device illuminates an image on a photosensitive drum. The video count acquisition refers to a state (S809) in which video count information is acquired from the exposure device for the purpose of determining the amount of toner to be supplied. The toner supply indicates steps (S811, S812) of driving a toner supply unit and supplying a required amount of toner to the developer container.
Once power is supplied to the main unit of the image forming apparatus and predetermined start-up preparations are completed, the image forming apparatus enters a standby state. When the image forming apparatus in such standby state receives a print signal, the image forming apparatus commences printing, activating in order the photosensitive drum, the charge device, the exposure device and so on. The developing apparatus remains stopped in a standby state until the timing needed for developing the image arrives and operates only when developing the image, rotating the developing sleeve and the screws. Then, video count measurements are carried out simultaneously with the activation of the exposure device, thus calculating the amount of toner to be supplied for the next printing operation.
At the next printing operation, toner supply is carried out based on the amount of toner supplied as calculated on the basis of the video count taken during the previous printing, thus maintaining the density of the toner inside the developing container at a constant level.
However, the above-described operations can give rise to the following problems.
First, since the video count is carried out while monitoring the exposure state of the exposure device, the measurement time lasts approximately as long as the processing time for the image forming apparatus, after which toner supply is carried out, which means that the timing of the rotation of the developing sleeve of the developing apparatus falls out of synch with the timing of the image forming apparatus. As a result, the supply of toner is always at least one page behind the printing. When that happens, those systems which store data on the toner supply amount in the RAM of the image forming apparatus lose that data when the power to the image forming apparatus is switched OFF and the RAM is reset, leading to a situation in which no toner is supplied to the first sheet to be printed after the power is turned ON again. In extreme cases, no toner is supplied at all if, repeatedly, only a single page is printed before the power is shut OFF once more.
Providing the image forming apparatus with a nonvolatile memory and recording in that memory the data needed to supply an amount of toner to the first page to be printed after the power is again turned ON can solve such a disadvantage. In most cases, however, by the time the power is turned on again the developer has been left to harden into a mass, so ordinarily the agitation device is first rotated in a warm-up operation in order to loosen the developer, and as a result the toner that should have been supplied for the first page of printing has already been ejected from the toner supply aperture during warm-up while a new supply of toner has not yet been delivered. The upshot is that there is no or insufficient toner left for the printing of the first page.
Another difficulty is that if the toner is delivered in a bunch to the dried-out developer, the toner and the developer will not be properly mixed and the charge will be unevenly distributed.
Additionally, in those image forming apparatuses in which the developing apparatus is in the form of a replaceable cartridge, it is always possible that the toner cartridge will be replaced while the power is OFF, which means that a completely unrelated toner supply may be conducted from a separate cartridge.
The present invention has been proposed to solve the problems of the conventional art, and has as its object to provide an image forming apparatus and an image forming method for a developer density control system that requires that toner supply be deferred until the next image formation operation whenever the amount of toner required to be supplied cannot be determined and the supply of toner cannot be completed within the time required for a single sheet to be printed, in which a special toner supply mode is executed whenever the power to the image forming apparatus is switched OFF such that the supply of toner is completed before the main power is switched OFF.
As a result of the execution of this special toner supply mode prior to the shutdown of power to the image forming apparatus, a situation in which too little toner or no toner at all is supplied during warm-up can be prevented because the image forming apparatus is continuously monitoring and adjusting the toner density so as to obtain optimum density levels.
The above-described object of the present invention is achieved by an image forming apparatus for controlling a toner supply, comprising:
density detecting means for detecting a density of toner in a developer when forming an image;
toner supply means for supplying toner during image formation in an amount determined by a first toner density detected by the density detecting means and stored in a memory;
image forming means for forming an image with toner supplied from the toner supply means in accordance with the toner density detected by the density detecting means and stored in the memory; and
storage means for storing in the memory a second toner density detected by the density detecting means in preparation for forming a second image after forming a first image,
the toner supply means shutting off power to the image forming apparatus after supply of toner to the image forming apparatus using the second toner density stored in the memory is completed when power to the image forming apparatus is switched OFF.
Preferably, the above-described image forming apparatus is one in which the density detecting means calculates a toner density decrease by determining the amount of toner consumed using a video count that integrates a number of laser drive clock pulses that correspond to a respective plurality of pixel densities of each image to be formed.
Preferably, the image forming apparatus is one in which the image forming means forms an image corresponding to color elements including yellow (Y), magenta (M), cyan (C) and black (Bk) in order to form a color image.
Preferably, the image forming apparatus is one in which the image forming means comprises:
an electrostatic potential image forming means for forming an electrostatic potential image, the electrostatic potential image forming means comprising:
charging means for charging the electrostatic potential image forming means so as to form the electrostatic potential image; and
developing means comprising:
a developer container for containing a two-part developer consisting of a toner and a carrier;
an agitation device for agitating the developer inside the developer container; and
a developer sleeve for holding and transporting the agitated developer to a developing unit; and
deletion means for deleting the electrostatic potential image formed by the electrostatic potential image forming means,
the developing means, the charging means and the electrostatic potential image forming means being formed into a single detachable cartridge structure signed to be mounted in the image forming apparatus.
Additionally, the above-described object of the present invention is achieved by an image forming method for forming an image by controlling a timing of toner supply, comprising:
a density detecting step for detecting a density of toner in a developer when forming an image;
a toner supply step for supplying toner during image formation in an amount determined by a first toner density detected in the density detecting step and stored in a memory;
an image forming step for forming an image with toner supplied in the toner supply step in accordance with the toner density detected in the density detecting step and stored in the memory; and
a storage step for storing in the memory a second toner density detected in the density detecting step in preparation for forming a second image after forming a first image,
the toner supply step shutting off power to an image forming apparatus after supply of toner to the image forming apparatus using the second toner density stored in the memory is completed when power to the image forming apparatus is switched OFF.
Preferably, the image forming method is one in which the density detecting step calculates a toner density decrease by determining the amount of toner consumed using a video count that integrates a number of laser drive clock pulses that correspond to a respective plurality of pixel densities of each image to be formed.
Preferably, the image forming method is one in which the image forming step forms an image for each color element, including yellow (Y), magenta (M), cyan (C) and black (Bk).
Additionally, the above-described object of the present invention is also achieved by an image forming program for causing a computer to control toner supply timing and execute an image forming method, the program comprising:
a density detection module for detecting and storing in a memory a first density of a toner in a developer during image formation;
a supply module for using the first toner density detected by the density detection module to adjust an amount of toner to be supplied during one image formation operation executed after the first toner density detected by the density detection module is stored in the memory;
an image formation module that forms an image using the toner supplied by the supply module as adjusted to an optimum toner density; and
a storage module for storing a second toner density detected by the density detection module in the memory in preparation for a succeeding image formation operation,
the program module causing the computer to shut off power to the image forming apparatus after supply of toner to the image forming apparatus using the second toner density stored in the memory is completed when power to the image forming apparatus is switched OFF.
Additionally, the above-described object of the present invention is also achieved by a computer readable recording medium containing a program module that causes a computer to control toner supply timing and execute an image forming method, the program module comprising:
a density detection module for detecting and storing in a memory a first density of a toner in a developer during image formation;
a supply module for using the first toner density detected by the density detection module to adjust an amount of toner to be supplied during one image formation operation executed after the first toner density detected by the density detection module is stored in the memory;
an image formation module that forms an image using the toner supplied by the supply module as adjusted to an optimum toner density; and
a storage module for storing a second toner density detected by the density detection module in the memory in preparation for a succeeding image formation operation,
the program module causing the computer to shut off power to the image forming apparatus after supply of toner to the image forming apparatus using the second toner density stored in the memory is completed when power to the image forming apparatus is switched OFF.
Additionally, the above-described object of the present invention is achieved by a computer into which a computer-readable recording medium containing a program module that causes the computer to control toner supply timing and execute an image forming method, the program module comprising:
a density detection module for detecting and storing in a memory a first density of a toner in a developer during image formation;
a supply module for using the first toner density detected by the density detection module to adjust an amount of toner to be supplied during one image formation operation executed after the first toner density detected by the density detection module is stored in the memory;
an image formation module that forms an image using the toner supplied by the supply module as adjusted to an optimum toner density; and
a storage module for storing a second toner density detected by the density detection module in the memory in preparation for a succeeding image formation operation,
the program module causing the computer to shut off power to the image forming apparatus after supply of toner to the image forming apparatus using the second toner density stored in the memory is completed when power to the image forming apparatus is switched OFF.
Additionally, the above-described object of the present invention is also achieved by an image forming apparatus that uses a developer having a toner and a carrier, the image forming apparatus comprising:
detecting means for detecting an amount of toner consumed during image formation;
mixing means for mixing the toner and the carrier; and
toner supply control means for controlling a supply of toner to the mixing means,
wherein the toner supply means controls the supply of toner during succeeding image formation operation according to the detected amount of toner consumed during a preceding image formation operation so as to adjust the density of the toner, and when the image forming apparatus is OFF, the toner supply means continuing to supply toner in the absence of an image formation operation using the detected amount of toner consumed during a last image formation operation before the image forming apparatus is actually OFF.
Additionally, the above-described object of the present invention is also achieved by the image forming apparatus as described above, wherein the detecting means detects the amount of toner to be consumed during an image formation operation using an image signal that expresses the image to be formed.
Additionally, the above-described object of the present invention is also achieved by the image forming apparatus as described above, further comprising image forming means for forming an image corresponding to color elements including yellow (Y), magenta (M), cyan (C) and black (Bk) in order to form a color image.
Additionally, the above-described object of the present invention is also achieved by the image forming apparatus as described above, further comprising:
a developer container for containing a two-part developer consisting of a toner and a carrier; and
an agitation device for agitating the developer inside the developer container.
Additionally, the above-described object of the present invention is also achieved by the image forming apparatus as described above, further comprising:
an image retention medium designed to retain an electrostatic potential image;
charging means for charging the image retention medium;
developing means including a developing sleeve for holding and transporting the developer mixture containing toner and carrier to a developing unit and developing an electrostatic potential image formed on the image retention medium so as to form a toner image; and
deletion means for deleting the toner image,
at least the agitation device, the image retention body, the charging means, the developing means and the deleting means being formed into a single detachable cartridge structure designed to be mounted in the image forming apparatus.
Other objects, features and advantages of the present invention besides those discussed above shall be apparent to those skilled in the art from the description of preferred embodiments of the invention that follows, with reference to the accompanying drawings.